The present invention relates to a novel electronic weft stop motion on a gripper shuttle weaving machine provided with a shuttle picking device, shuttle catching means including shuttle braking and resetting means, and thread tensioning means in advance of the shuttle picking device for laterally deflecting the weft yarn during the action of the shuttle resetting means.
A gripper shuttle weaving machine and weft stop motions fitted thereto are described in German patent publication No. 1,535,615. Weaving machines of this type are generally known and in widespread use. Essential for the function of the weft stop motion or weft thread monitor in this case is the cooperation of the elements effecting the weft insertion, in particular the gripper shuttle or projectile, a thread brake located on the picking side and a subsequently arranged thread tensioner. This weft thread monitor responds to the so-called pull-after motion of the weft thread which occurs in the last phase of the lateral deflection thereof: when the weft thread inserted in the weaving shed has been tensioned, a small thread end is pulled through the thread brake in a direction from the supply spool of the weaving machine. According to a preferred embodiment, a roller is provided as thread feeler and arranged in the region of lateral deflection. Rotation of the roller is sensed and indicated by an optoelectrical sensor. The roller comes into contact with the weft thread only upon lateral deflection thereof without at first being set into rotation. After that the roller is rotated when the pull-after movement begins, and the sensor responds and produces a signal indicative of an intact weft thread. A particular trigger device controlled by the weaving machine delimits the response of the weft thread monitor to a time interval defined by the pull-after motion. Absence of the sensor signal within this time interval causes the weaving machine to stop.
With this known weft stop motion, the late monitoring when the weft thread has already been inserted is advantageous since disturbances, such as thread breaks, which do not seldomly occur in the last phase of the weft insertion are detected. On the other hand, a very small time interval is available for the timely or correct stopping of the weaving machine, and the inertia of the roller feeler is detrimental in this respect. Moreover, the pull-after motion may fail to appear even with an intact or correctly inserted weft thread; in this event the weft thread monitor causes an unwanted or faulty stop of the weaving machine.